1. Field of the Invention
The present invention relates to a method for operating a surroundings-detection system of a vehicle, which includes at least one transceiver unit, which emits signals and receives echo signals of the emitted signal. The present invention also relates to a computer program and a surroundings-detection system, which is configured to carry out the method.
2. Description of the Related Art
Ultrasonic-based measuring systems are used for measuring a distance to an object situated in front of a sensor system. The sensors used in this case are based in most cases on a pulse/echo method. In this operation, the sensor emits an ultrasonic pulse and measures a reflection of the ultrasonic pulse generated by an object, which is referred to as an echo signal. The distance between the sensor and the object is computed over the measured echo transit time and the speed of sound. In addition to the distance of the object to the sensor, the speed of the object relative to the sensor system is also of interest for the surroundings-detection. Due to the Doppler Effect, a frequency shift of the echo frequency occurs relative to the transmission frequency. The speed of the object relative to the sensor system may be ascertained by the frequency shift in systems, which are based on the pulse/echo method.
Published European patent application document EP 1 248 119 A1 shows a method for detecting signals in systems subjected to an unknown Doppler frequency shift, which adversely affects modulated coherent signals, which are used, for example, for distance measuring purposes. A coherent demodulator processes the received signal in the receive filter path in order to reconstruct a time-delayed replica of the modulated waveform. The modulated waveform and its time-delayed replica are processed in a correlator in order to determine the distance between the system and an obstacle. In a relative movement between the system and the obstacle, the value of the frequency shift is determined from
      ω          D      0        =                    2        ⁢                  v          0                    c        ⁢          ω      0      
The Doppler frequency ωDO is computed from a rate of change of a correlation function, which is repeatedly computed for successive short processing intervals. EP 1 248 119 A1 relates to systems which operate in the microwave range.
Published German patent application document DE 195 33 126 A1 shows a Doppler sensor for detecting the movement of an object in a defined distance range, a signal source being provided, which generates a microwave signal with which a suitable code signal, for example, a chirp signal, is mixed and emitted. The signal reflected by an object and received is fed to a correlator in order to correlate it with the code signal delayed by a delaying element.